Hitherto, there has been known an electrostatic copying apparatus of the type in which, with the aim of machine compacturization and otherwise, it is arranged that a high voltage trigger is applied to an electrostatic charger and to an image transferring charger by a common high-voltage trasnformer.
Generally, in electrostatic copying apparatuses, the process of copying is carried out in such a way that the surface of a photoreceptor to which an electrostatic charge is applied by an electrostatic charger is exposed to a light image of an original so that an electrostatic latent image is formed on the surface of the photoreceptor; and in a subsequent developing stage the electrostatic latent image is developed into a toner image which, in turn, is transferred onto a copying sheet as an image transferring charger is actuated into operation in the stage of image transferring.
In this way, it is required that after an electrostatic latent image has been formed on the photoreceptor, the transferring charger be actuated in the transferring stage which follows the stage of developing. Therefore, in the electrostatic copying apparatuses of the above mentioned arrangement wherein a high voltage trigger is applied to both the electrostatic charger and the transferring charger simultaneously by the common high-voltage transformer, electrostatic discharge from the electrostatic charger is continued even during the stage of image trasferring.
In other words, a non-image area located behind an image area in which the electrostatic latent image has been formed in continuously subjected to electrostatic charging by the electrostatic charger.
Therefore, in order to prevent toner particles fed from a developing device from adhering to the electrostatically charged non-image area, it is necessary to subject the non-image area to the step of so-called blank exposure thereby to remove the charge from the non-image area. Such blank exposure is also executed prior to the formation of an electrostatic latent image in each copying cycle for purposes of removing a residual charge in the previous copying cycle and otherwise.
Now, an electrostatic copying apparatus has been proposed which has a movable shutter adapted to be inserted into and retracted from an optical path between an original and a photoreceptor, whereby the movable shutter is inserted into the optical path during the stage of blank exposure so that it operates to cause a beam of light from a light source to be reflected toward the surface of the photoreceptor, the charge on the photoreceptor surface being thereby removed (see Japanese Patent Application Laid-Open Publication No. 54-58447). This arrangement eliminates the necessity of providing an independent source of light for blank exposure.
According to the arrangement of such a copying apparatus, it may be possible to utilize the movable shutter when a high voltage trigger is applied to both the electrostatic charger and the image transferring charger by the common high-voltage transformer, so that a beam of light from the light source is projected onto the surface of the photoreceptor through the movable shutter in order to remove the charge applied to the surface of the photoreceptor by the electrostatic charger during the stage of image transferring.
The use of such movable shutter eliminates the need for an independent light source for blank exposure. On the other hand, however, the trouble is that since the movable shutter itself is rather complicated in construction, the provision of the movable shutter complicates the construction of the image forming apparatus, and further entails an increase in manufacturing cost.